1. Field of the Invention
The present invention relates to a data recording/reproducing apparatus, a data recording/reproducing method and a data format, in particular to, a data recording apparatus, a data recording/reproducing method and a data format suitable for inputting/outputting high quality video data on many channels.
2. Description of the Prior Art
Generally, in a data recording/reproducing apparatus such as a hard disk drive that randomly accesses data, data is asynchronously transmitted. In such a data recording/reproducing apparatus, a reproduction signal is processed with a clock signal reproduced from a disk that rotates. However, the rotation of the disk does not synchronize with a reference signal. In recently, some data recording/reproducing apparatuses have a structure of which the rotation of the disk synchronizes with an external signal. However, an interface of these apparatuses inputs/outputs data (generally, for example SCSI interface) with a common line for transmitting commands and data. Thus, the data transmission varies depending on data exchanged between an initiator and a target.
In addition, to improve the record density of hard disks, data record frequencies are varied corresponding to the record positions thereon. Thus, when a plurality of hard disk drives are operated, reproductions signals thereof may not synchronize with each other.
Thus, when data transmission rate or storage capacity is increased with a plurality of hard disk drives, data supplied from each hard disk drive should be temporarily stored in for example a memory and read as blocks.
However, in the case that such a process is performed with a data recording/reproducing apparatus that requires high picture quality, when data is recorded for a long time, high data transmission rate and large storage capacity are required. Thus, the number of hard disk drives should be operated in parallel increases.
For example, video data of for example D2 base band requires an execution transmission rate of around 120 Mbps per channel. When the transmission rate per hard disk drive is around 24 Mbps, five hard disk drives are required. For example, when the number of channels is six, 30 hard disk drives are required.
The execution transmission rate is a value of which a predetermined data amount is divided by a total time period necessary for reading/writing the data amount. In other words, the execution transmission rate is not a transmission rate of a hard disk drive, nor an instantaneous transmission rate of an interface portion. In addition, it is assumed that on each channel, a plurality or the same picture of the same recording/reproducing apparatus is reproduced or recorded.
However, it is not common to operate as many as 30 hard disk drives in parallel. When a number of hard disk drives are operated at the same time, the load of a portion that issues commands and manages the hard disk drives becomes large. Thus, since the process of this portion takes a long time, the execution transmission rate decreases or the reliability against failures of the hard disk drives deteriorates.
Conventionally, to solve such a problem, an apparatus is divided into a plurality of disk arrays. Data is distributed to a plurality of hard disk drives. In addition, parities calculated with the data are also used to secure redundancy. By operating a plurality of disk array units in parallel, the transmission rate is increased.
FIG. 1 is a schematic diagram showing the structure of a conventional disk array unit. As shown in FIG. 1, in the conventional disk array unit, a plurality of hard disk drives are connected to a disk array controller 101 (in this example, six hard disk drives 110 to 115 are connected). The hard disk drives 110 to 114 are used to record data. The disk array controller 101 assigns input data to the hard disk drives 110 to 114. The hard disk 115 records only parities calculated with the input data.
To increase the transmission rate and storage capacity, a data recording/reproducing apparatus having a plurality of disk array units that operate in parallel has been proposed. FIG. 2 shows an example of the structure of this data recording/reproducing apparatus.
As shown in FIG. 2, in the conventional data recording/reproducing apparatus, video data controllers 201 are disposed corresponding to individual channels. Buffer memories 210 to 215 corresponding to individual disk array units 220 to 225 are connected to the video data controller 201. The buffer memories 210 to 215 of each channel are connected to individual disk array units 220 to 225 by a SCSI interface. The structure of each of the disk array units 220 to 225 is the same as the structure of the conventional disk array unit shown in FIG. 1.
However, in the conventional data recording/reproducing apparatus, a reproduction request issued by the video data controller 201 to the disk array units 220 to 225 does not chronologically synchronize with data obtained from the disk array units 220 to 225. Thus, to synchronize these data and restore data of one channel, the buffer memories 210 to 215 corresponding to the disk array units 220 to 225 for each channel and a memory control circuit (not shown) for the buffer memories 210 to 215 should be disposed. To prevent video data from discontinuing, the video data controller 201 should always monitor the data amount of the buffer memories 210 to 215 and issue a data transmission request to the disk array units 220 to 225 when the data amount decreases to a predetermined level. Thus, the structure of the data recording/reproducing apparatus becomes complicated and the cost thereof increases.
In addition, the apparatus should control the video data controllers 201 so that they do not issue commands to the disk array units 220 to 225 at the same time. Thus, since the use efficiency of the bus decreases, it is difficult to raise the execution transmission rate. In addition, although the disk array units 220 to 225 and the video data controller 201 are connected with a SCSI interface that has been commonly used as a standard hard disk drive interface, the SCSI interface is basically shared by a signal input and a signal output. Thus, when a record request and a reproduction request are issued from video data controllers 201 of different channels, a time to change the transmission direction is required. Thus, the transmission rate deteriorates.
In addition, for the SCSI interface, a 68-pin cable is required (depending on the applied standard, at least 50 pins are required). To construct a large-scaled system, a number of cables are required. In addition, since a number of connection points are required, the reliability deteriorates. Moreover, a large cabinet is required for the mounting area of the connectors. To transmit parallel data for a long distance, many drivers are required. Thus, the number of devices of the circuitry increases. Consequently, the area for the devices becomes large.